The present invention relates to weighted elastomers and, more particularly, in certain embodiments, to weighted elastomers, cement compositions comprising weighted elastomers, and methods of using weighted elastomers in cementing operations.
Cement compositions may be used in a variety of subterranean applications. For example, in subterranean well construction, a pipe string (e.g., casing, liners, expandable tubulars, etc.) may be run into a well bore and cemented in place. The process of cementing the pipe string in place is commonly referred to as “primary cementing.” In a typical primary cementing method, a cement composition may be pumped into an annulus between the walls of the well bore and the exterior surface of the pipe string disposed therein. The cement composition may set in the annular space, thereby forming an annular sheath of hardened, substantially impermeable cement (i.e., a cement sheath) that may support and position the pipe string in the well bore and may bond the exterior surface of the pipe string to the subterranean formation. Among other things, the cement sheath surrounding the pipe string should function to prevent the migration of fluids in the annulus, as well as protecting the pipe string from corrosion. Cement compositions also may be used in remedial cementing methods, for example, to seal cracks or holes in pipe strings or cement sheaths, to seal highly permeable formation zones or fractures, to place a cement plug, and the like.
Elastomers are one additive that may be included in a cement composition. Among other reasons, elastomers may be included in a cement composition to improve the mechanical properties of the set cement composition. For example, elastomers may be included in a cement composition to improve the elasticity and ductility of the set cement composition, thereby potentially counteracting possible stresses that may be encountered by the cement composition in a well bore. In some instances, elastomers that swell upon contact with water and/or oil may be used. These swellable elastomers may help maintain zonal isolation, for example, by swelling when contacted by oil and/or water to seal cracks in the cement sheath and/or micro-annulus between the cement sheath and the pipe string or formation that may be created.
Weighting agents also may be included in the cement compositions to increase the density of the cement composition. A cement composition having an increased density may be desirable, for example, in deep wells where high pressure may be encountered. Examples of weighting agents that may be used include, but are not limited to, hematite, hausmannite, barite, and sand.
A problem often encountered when both elastomers and weighting agents are included in a cement composition is that the elastomers and weighting agents tend to segregate in different areas of the cement composition. For example, the weighting agents generally tend to sink while the elastomers tend to float, which can leave certain areas with little or no weighting agent and other areas with little or no elastomer. As a result, the cement composition may not have a uniform density distribution when introduced into the formation, resulting in a potential for the design specifications of the cement composition to not be met. To prevent this undesired segregation, great care is often taken in formulating cement compositions that comprise both elastomers and weighting agents. This may result in added expense and complexity due to, among other things, a need for additional additives and monitoring.